Encountered some problem in this question....

Hi! i used your website to refresh my math skill and it's good so far until i encountered an error in this question about remainder and factor theorem here's the link: http://www.mathopolis.com/questions/q.php?id=231&site=1&ref=/algebra/polynomials-remainder-factor.html&qs=0

i tried to solve the problem and come up with the answer a = 1, b = -4, c = -4 but the answer is not there and i tried to pick a random answer so i can see the correct answer and the correct answer is b, but when i substitute the value to the given equation the result is not equals to 0 here's how i checked it :